Aspiration system for removing liquid other than urine discharged by the human body

ABSTRACT

An aspiration system for removing liquid other than urine, which liquid is discharged from the human body, comprises a disposable body interface device having a liquid collection chamber. A liquid sensor detects the presence of liquid within the chamber, and controls application of aspiration suction to remove liquid from the liquid collection region. The body interface device may be a wound dressing, and the liquid wound exudate. The aspiration suction is controlled to remove only excess wound exudate.

FIELD OF THE INVENTION

The present invention relates to an aspiration system for use inremoving liquids discharged by the human body. The invention may be usedfor removing body fluids and secretions other than urine. One aspect ofthe invention relates to removal of wound exudate.

BACKGROUND TO THE INVENTION

Wound exudate can be described as the liquid produced from chronicwounds, fistula, or acute wounds once haemostasis has been achieved. Forcenturies, the production of exudate was regarded as inevitable withcertain types of wound, and inconsequential with respect to woundhealing.

More recently, considerable attention has been given to the developmentof wound dressings that prevent the accumulation of large volumes offluid within a wound, and also prevent the fluid from spreading over thesurrounding healthy tissue. This is because excessive wound exudate cancause maceration of the peri-wound skin, which in turn can lead toinfection. One technique known in the art is the application of suctionto create negative pressure at the wound site, as taught in U.S. Pat.Nos. 4,969,880, 5,636,643, 5,645,081, 7,216,651, and U.S. PatentPublication No. 2001/0029956. Negative pressure means pressure belowsurrounding atmospheric pressure. Such a technique is referred to in theart as Topical Negative Pressure (TNP). This is believed by someresearchers to aid drainage of wound exudate away from the wound bed,reduce infection rates, and increase localized blood flow.

The prior art arrangements are said to permit medical staff to manuallyadjust the duty cycle times of the application of suction. However, iftoo much suction is applied, complications occur diminishing thebenefits of the wound dressing. In particular:

(i) The negative pressure tends to draw tissue growth into the pores ofa foam piece inside the wound dressing. This can result in discomfort tothe patient during use of the device, and both discomfort and potentialnew tissue damage upon removal or changing of the dressing.

(ii) The wound is vulnerable to drying out of wound exudate. Thiscondition is undesirable because exudate is now believed to contain acomplex mixture of bioactive molecules that have both positive andnegative effects. While removal of excess exudate is desirable, removalof all exudate may hinder rather than aid wound healing. Proper use ofthe wound dressing may depend to a large extent on the expertise ofmedical staff in assessing the rate of production of wound exudate atthe wound site, and adjusting the suction accordingly. If frequentremoval of the dressing is required to assess the state of the wound andexudate, this merely exacerbates discomfort caused by drawback (i)above.

Some of the drawbacks may be partly mitigated by the use of hydro-fiberas described in U.S. Patent Publication No. 2006/0100594. However, thisdoes not solve the root problem.

The present invention has been devised bearing such issues in mind.

SUMMARY OF THE INVENTION

Aspects of the invention are defined in the claims.

In a further broad aspect, an aspiration system and method are providedfor removing liquid other than urine, which liquid is discharged fromthe human body. The system comprises a disposable body interface devicehaving a liquid collection chamber. A liquid sensor detects the presenceof liquid within the chamber. The application of aspiration suction toremove liquid from the liquid collection region is controlled responsiveto the output of body fluids and secretions detected by the liquidsensor. The body interface device may be a wound dressing to allowcontrolled draining of the liquid wound exudate. The aspiration suctioncan be controlled to remove only excess wound exudate, according to theoutput of body fluids and secretions detected by the liquid sensor.

While certain features and ideas are emphasized above and in theappended claims, the Applicant may seek claim protection for any novelfeature or idea described herein and/or illustrated in the drawings,whether or not emphasis has been placed thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a first embodiment of aspirationsystem for collecting and removing liquid wound exudate discharged by awound of the human body, the diagram including an exploded sectionalview of the wound dressing components.

FIG. 2 is a schematic sectional view showing, in exploded form, amodification of the wound dressing from FIG. 1.

FIG. 3 is a schematic diagram showing operation of the aspiration systemin graphical form.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the invention are now described with referenceto the drawings. The same reference numerals are used to depict the sameor equivalent features in each embodiment.

Referring to FIG. 1, an aspiration system 10 for removing body liquid(other than urine) discharged or secreted by the human body generallycomprises: a body interface device 14; and an aspiration unit 12 forapplying suction to the body interface device 14 to aspirate the bodyliquid. The present embodiment illustrates an aspiration system 10specifically for removal of wound exudate from a wound site 18. The bodyinterface device 14 is in the form of (and is hereafter referred to as)a wound dressing, configured for fitting to the body at, or around, thewound site 18. The field of wound dressings with exudate aspiration isquite unique, and very different from the field of, for example, urineremoval. Urine is usually discharged as a gush of liquid, and a urineremoval system should remove all urine to leave the skin dry in order toavoid irritation and infection. In contrast, wound exudate is notdischarged in a gush, and it is not desirable to remove all of the woundexudate. The exudate contains a complex mixture of bioactive moleculesthat have both positive and negative effects. While removal of excessexudate is desirable, removal of all exudate may hinder rather than aidwound healing. Instead, the present embodiment aims to manage the amountof wound exudate, and remove excess from the wound site.

As explained in more detail later, such management is facilitated inaccordance with the principles of the invention by provision of a liquidsensor 30 for detecting liquid exudate in the wound dressing 14. Theliquid sensor 30 generates a signal 32 indicative of sensed liquid. Thesensor 30 may detect one or both of the following parameters: (i)proximity of liquid, and/or (ii) a quantity of liquid within sensingrange. The aspiration unit 12 is responsive to the sensor signal 32 inorder to control the application of aspiration suction. Such anarrangement provides the extremely significant advantage of being ableto control the aspiration of wound exudate automatically, to removeexcess exudate while preserving a desired residual quantity of exudatewithin the wound dressing without drying out the wound.

The constitution of the aspiration system 10 is now described in moredetail. The wound dressing 14 is preferably attachable to the patient'sskin 20 by means of an adhesive pad 26. In the form illustrated in FIG.1, the adhesive pad 26 has a closed loop shape that circumscribes theperiphery of the wound site 18. In the form illustrated in FIG. 2, theadhesive pad 26 extends over the wound site 18, and has perforations orapertures 27 to permit passage of exudate from the wound site 18 intothe wound dressing 14. The adhesive pad 26 is made of a skin-friendlymedical grade adhesive. Examples of suitable adhesives includepressure-sensitive adhesives that may be any of hydrocolloid,polyurethane, acrylic, thermoplastic elastomer (TPE), hydrogel, orsilicone-based.

The wound dressing 14 may have any suitable construction for coveringthe wound site 18, defining a liquid collection region and at leastpartly a local environment conducive to wound healing. For example, thewound dressing 14 may be the same as, or similar to, the dressings shownin any of the aforementioned U.S. Pat. Nos. 4,969,880, 5,636,643,5,645,081, 7,216,651, and/or U.S. Publication Nos. 2001/0029956 and2006/0100594. The wound dressing 14 typically comprises a cover 16extending over the wound site 18, and overlapping healthy peri-woundtissue. The wound dressing 14 may optionally contain or comprise aliquid handling material 24 (24 a, 24 b). The liquid handling material24 may, for example, be a material for absorbing exudate withoutgelling. Such a material may be non-woven and/or a foam. Such anon-woven material could be hydrophobic or hydrophilic, synthetic ornatural. The liquid handling material 24 may alternatively be, orcomprise, a fibrous blend or fibrous material (e.g., a non-woven) thatforms a cohesive gel when wetted with wound exudate. Such a fibrousmaterial can be provided, for example, by the wound contact layer of theVersiva® dressing (ConvaTec Inc., Skillman, N.J.) or by a fibrous mat ofsodium carboxymethylcellulose. A fibrous mat of sodiumcarboxymethylcellulose is available as AQUACEL® dressing from ConvaTecInc., as is a similar dressing further including silver. Other exemplarymaterials for the liquid handling material 24 include Medicel™,Carboxflex™ (which provides an odor absorbent layer with fibrousmaterial for wicking liquid away from the odor absorbent), Hyalofill™(forming a hyaluronic acid-rich fibrous gel) or Kaltostat™ (containingalginate) dressings from ConvaTec Inc. While the liquid handling layer24 has the ability to absorb the exudate quickly, it also allows exudateto be pumped away under suction.

In a further form, a combination of both a non-gelling liquid handlinglayer 24 a and a fibrous gelling layer 24 b may be used, for example, indistinct layers. The layers 24 a and 24 b may be bonded to each other,or they may be contained as separate layer components within the wounddressing 14. FIG. 1 illustrates an optional perforated screen 28 thatmay be used, for example, to enclose such layers 24 a and 24 b.Furthermore, liquid handling layer 24 b maybe perforated to allow excessexudate to be absorbed by liquid handling layer 24 a.

An aspiration source connector 22 (e.g. silicone tubing) extends intothe wound dressing 14 for delivering aspiration suction from theaspiration unit 12. In the form illustrated, the connector 22 extendsthrough the cover 16, although the connector 22 could enter the wounddressing 14 at any suitable point. Preferably, the point at whichsuction is applied is separated from the wound site 18 by at least aportion of the liquid handling material 24. In the preferred formincluding both non-gelling and gelling layers 24 a, 24, respectively,the point at which suction is applied is spaced from the wound site 18by at least the gelling layer 24 b, and preferably also by at least aportion of the non-gelling layer 24 a.

A flexible conduit 35 couples the wound dressing 14 to the aspirationunit 12. A releasable connector or an easy release coupling may beprovided at one end, or both ends, of the conduit 35. The flexibleconduit 35 may be regarded as part of the aspiration unit 12 and/or partof the body interface device 14. The flexible conduit 35 links theconnector 22 to a suction source 40 within the aspiration unit 12. Theaspiration unit 12 comprises a power supply 38, an electronic controlunit 44, and the suction source 40. The power supply 38 is selected asone or more of: a replaceable battery, a rechargeable battery, radiationcollection panels, and a mains power supply. Preferably, the powersupply 38 includes a combination of a rechargeable battery and a mainspower supply; such a combination allows portable operation when theaspiration system 10 is not connected to a mains power supply, as wellas automatic recharging of the battery when the aspiration system 10 iscoupled to a mains power supply. Additionally or alternatively, thepower supply 38 includes radiation collection panels, such asphotovoltaic panels or cells for generating electricity from ambientlight, which can improve autonomy of operation or for charging therechargeable battery. The power supply 38 may provide power for any oneor more of: the electronic control unit 44, the liquid sensor 30 (ifneeded) and any power needed by the suction source 40. In the presentembodiment, the suction source 40 is an electric pump that operatesunder control of the electronic control unit 44. The pump 40 could be asuction device based on diaphragm, peristaltic, volume displacement,spring, gravity, siphon, heat-recoverable metal drive, or an in-linepump. The flexible conduit 35 is coupled through the pump 40 to a liquidcollection chamber 42 for collecting exudate removed from the wounddressing 40. The liquid collection chamber 42 may either be separatefrom the aspiration unit 12 (as illustrated) and coupled thereto with asuitable connector, or the liquid collection chamber 42 may be integralwith and/or housed in the aspiration unit 12 (arrangement not shown). Inan alternative form, instead of a pump 40 directly applying suction tothe flexible conduit 35, the suction source 40 may comprise a vacuumchamber charged with a low pressure vacuum, and an electronicallycontrolled valve for controlling application of suction from the vacuumchamber to the flexible conduit 35. A pump may be provided for chargingthe vacuum chamber with the vacuum.

The liquid sensor 30 may be separate or separable from the wounddressing 14, enabling replacement of the wound dressing 14 withouthaving to use a new sensor 30. In such a case, a means is preferablyprovided for releasably attaching the sensor 30 to the wound dressing14. Alternatively, the liquid sensor 30 may be permanently attached tothe wound dressing 14 to form an integral unit. With permanentattachment, the liquid sensor 30 is intended to be disposed of with thewound dressing 14.

The sensor signal 32 is typically an electrical or electronic signal.However, other signal forms may be used as desired, for example,optical.

The sensor 30 may generate output signal 32 that varies in accordancewith the sensed parameter(s). For example, the output signal 32 may be avarying analog signal (e.g., variable current or voltage), or the outputsignal 32 may be a digital signal (e.g., a quantized representation, ora variable pulsed representation). Alternatively, the output signal 32may be a logical (e.g., binary, or on/off) signal indicating whether ornot the sensed parameter exceeds or is below one or more thresholds.

The liquid sensor 30 is preferably a non-contact sensor that is able todetect the presence or proximity of liquid without contact with theliquid. The liquid sensor 30 generates an electrical output signalresponsive to proximity of detected liquid. The electrical signal iscommunicated to the aspiration unit 12 either via the conduit 35, or viaa separate wire or wireless connector. A wired electrical connector mayalso supply power from the aspiration unit 12 to power the liquid sensor30.

The feature of the liquid sensor 30 being a non-contact sensor providessignificant advantages because: (i) the non-contact approachautomatically avoids any concerns about passing an electrical currentthrough liquid in contact with the skin 20 and wound site 18. Instead,there is no direct contact between the liquid sensor 30 and the liquid;(ii) the non-contact approach means that the liquid sensor 30 is notcontaminated by touching the liquid exudate. This allows the liquidsensor 30 easily to be reused with a different wound dressing 14; and(iii) the non-contact approach means that the liquid sensor 30 does notitself have to be in a sterile condition before use, thus avoiding thedifficulty of, or risk of damage when, sterilizing the aspiration system10 that does interface intimately with the body. The feature of theliquid sensor 30 being coupled to the aspiration unit 12 by anelectrical connector avoids the expense and fragility associated withusing an optical fiber connection.

An optional feature of the invention is that the liquid sensor 30 isseparate from, or at least separable from, the wound dressing 14. Thewound dressing 14 may be a disposable item that may be manufacturedinexpensively, and disposed of after a single use, or a limited numberof uses. The liquid sensor 30 may be more expensive, but may be intendedto be used plural times, preferably, with a sequence of different wounddressings 14 used during wound treatment. This enables the aspirationsystem 10 to be produced and used very cost efficiently, since thedisposable components are generally low cost. The higher cost componentsmay be used multiple times, and may require infrequent replacement. Inone form, the liquid sensor 30 is a universal device that may be usedwith any of a plurality of different types of wound dressings 14

Alternatively, the non-contact sensor may be permanently attached to thewound dressing 14, and not be a re-usable item.

The liquid sensor 30 can take a variety of different forms.

The liquid sensor 30 is selected from: a capacitance sensor; anultrasonic sensor; and a piezo-electric (or piezo-resonant) sensor. Acapacitance sensor detects proximity of liquid according to changes inthe dielectric effect of liquid proximity, compared to air proximity.The dielectric effect affects the electric field in the active zonearound the sensor, and thus, the effective capacitance in the sensor.The capacitance is monitored by any suitable capacitance sensing circuit(not shown), such as an RC oscillator whose oscillation frequency and/orwhether oscillation occurs, is dependent on the value of a resistor incombination with the effective capacitance of the sensor. Theoscillation in turn triggers an output stage, coupled to an outputamplifier, to generate an output signal indicative of liquid presence.The capacitance sensing circuit is preferably disposed near or at theliquid sensor 18 (e.g., as part of the liquid sensor 18 itself), or thecapacitance sensing circuit can be disposed at the aspiration unit 12,or at a point along electrical connector 35. A suitable capacitancesensor and capacitance sensing circuit are described in U.S. Pat. No.5,576,619, the contents of which are hereby incorporated by reference.

The ability to detect liquid has been tested using a capacitance “smart”sensor from SIE Sensors. The sensor 30 of dimension 35 mm (length)×22 mm(width)×10 mm (height) was affixed to the external wall of a bodyinterface device 14. The sensor 30 detected the presence of two testliquids, water and saline solution, as soon as the liquid wasintroduced, and provided an activation signal to the aspiration unit 12within milliseconds. The electric field from the sensor 30 is able topenetrate a wide variety of plastic components (e.g., polyethylene (PE),polypropylene (PP) and acrylics), either transparent or opaque, withgreat sensitivity.

An ultrasonic sensor works using the principle of sonar at theultrasonic frequency range. A transducer is resonated at a set frequencyto convert electric energy into ultrasonic frequency range acousticenergy. The ultrasonic acoustic waves are emitted towards a liquidcollection region. Energy is reflected either from the walls if theregion is empty of liquid, or from liquid if present in the region. Bymeasuring the time delay for reflected waves to arrive, and comparingthis to one or more pre-calibrated time delays taken when the liquidcollection region is empty, the presence of liquid can be reliably andquickly detected. An example of ultrasonic liquid sensor is described inU.S. Pat. No. 3,960,007, the content of which is incorporated herein byreference. A commercially available ultrasonic sensor is made availableby ZEVEX Inc.

A piezo-electric or piezo-resonant sensor also uses high frequency,e.g., ultrasonic energy or acoustic signal, in a similar way to theultrasonic sensor described above. The ultrasonic or acoustic signalcould penetrate either transparent or opaque plastic walls. An exampleof piezo-electric sensor is described in U.S. Pat. No. 3,948,098, thecontent of which is incorporated herein by reference.

The ability to detect liquid has been tested with a piezo-resonantsensor obtained from GEMS Sensors. The sensor 30 of diameter 40 mm wasattached to the external wall of the body interface device 14, anddetected the presence of liquid as soon as introduced.

With the arrangement illustrated in FIGS. 1 and 2, the liquid sensor 30is disposed outside the wound dressing 14, or at least outside a liquidcollection region of the wound dressing 14. The cover 16 is typicallymade of material through which the sensing electric field can pass inthe case of a capacitance sensor, or through which an ultrasonicvibration can pass in the case of an ultrasonic and/or piezo-electricsensor. The cover 16 may be made suitably thin to provide the sensor 30with the desired sensitivity to liquid within the body interface device14. Alternatively, the cover 16 may include a window portion made ofmaterial through which the electric field or ultrasonic vibration canpass easily if the entire cover 16 is not made of such a material. In analternative embodiment, the housing of the wound dressing 14 can beshaped into a pocket with or without membrane, for receiving andretaining a capacitive, ultrasonic or piezo-electric non-contact liquidsensor 30. Such a design also increases the interface area between thesensor 30 and the liquid collection region of the wound dressing 14.

In an alternative embodiment, the sensor 30 is an electro-opticalsensor. The cover 16 comprises a window region (not shown) made ofmaterial that is transparent to the optical radiation used by theelectro-optical sensor. For example, the optical radiation may be in theinfra-red range, and/or the visible range, and/or ultra-violet range.The term “optical” as used herein means that the radiation lies in afrequency range that obeys substantially the laws of optics. Theelectro-optical sensor comprises an electro-optical emitter, anelectro-optical receiver, and sensing circuitry for detecting thepresence of liquid according to the electrical output of theelectro-optical receiver. The sensing circuitry is preferably disposedat the liquid sensor 30 (e.g., as part of the liquid sensor 30), or thesensing circuitry is disposed at the aspiration unit 12, or at a pointalong electrical connector 35. An example electro-optical liquid sensoris described in U.S. Pat. No. 4,354,180, the content of which isincorporated herein by reference.

If preferred, the liquid sensor may be disposed at a position 30a incontact with exudate inside the wound dressing 14, even if the sensor 30does not rely on direct contact to detect the liquid. Such a possibilityalso enables the use of a contact-based sensor 30 instead of anon-contact sensor 30. An example of a contact-based sensor 30 is anelectrical resistance sensor that detects liquid by conductance betweenelectrodes in contact with the liquid.

In the case that the liquid sensor 30 is separate from, or at leastseparable from, the wound dressing 14, the liquid sensor 30 may be heldin an operative position with respect to the wound dressing 14 by adetachable attachment device (not shown) for releasably attaching theliquid sensor 30 to the wound dressing 14. For example, the detachableattachment device could comprise a peelable adhesive, or a peelablemechanical fastener, such as Velcro, or a mechanical coupling based oninterference fitting, or other mechanical means.

As mentioned previously, a goal of this embodiment is to manage woundexudate, so that excess exudate is removed efficiently while leaving aresidual amount of exudate in the wound dressing 14. Referring to FIG.3, when the wound dressing 14 is first fitted, the amount of woundexudate in the dressing 14 will rise progressively from zero as exudateis accumulated (for example, in the material(s) 24). The sensor 30 andthe control unit 44 co-operate to control the suction source 40 to keepthe amount of exudate at a desired level. While the level could beindicated by a single threshold, preferably two thresholds THR-on andTHR-off are used to introduce hysteresis to avoid the pump 40 beingswitched frequently. The upper threshold THR-on defines a threshold atwhich the pump 40 is switched to an aspiration mode (e.g., turned-on),and the lower threshold THR-off defines a threshold at which theaspiration is reduced or deactivated (e.g., pump 40 turned off), to stopfurther substantial remove of exudate. The amount of wound exudate willtherefore fluctuate between the two thresholds, with the pump 40 beingswitched at successive time points T1, T2 and T3, for example.

The thresholds THR-on and THR-off may optionally be adjusted manually bymeans of a manual control 46 of the aspiration unit 12. This may allowmedical practitioners to control variably the “wetness” of the woundsite 18, and allow different healing environments to be established asdesired by a medical practitioner. The control 46 may enable boththresholds to be adjusted. Alternatively, one of the thresholds may befixed at a predetermined level. Alternatively, the difference betweenthe thresholds may be variable, or may be fixed at a predeterminedlevel.

The control unit 44 may function to apply the thresholds to the sensorsignal 32. Alternatively, the sensor 30 itself may apply the thresholds,such that the output signal 32 is already thresholded. The sensitivityof the liquid sensor 30 may also be controlled by suitable positioningof the liquid sensor 30 with respect to the liquid handling material(s)24 of the wound dressing 14 and/or by the thickness of the cover 16 inreducing the sensing field of the sensor 30. In one form, it might notbe necessary to apply the lower threshold THR-off electronically.Instead, the sensor 30 may be sufficiently insensitive to liquid amountsbelow the threshold THR-off. Such an arrangement may be especiallysuitable when water-gelling material is used as the liquid handlingmaterial 24.

It will be appreciated that the aspiration system 10 as described hereinprovides significant advantages compared to the prior art, and canaddress or mitigate many of the drawbacks of the prior art, especiallyin terms of efficient aspiration of wound exudate, without drying outthe wound site 18, and without requiring frequent changes of the wounddressing 14 to inspect the degree of wetness of the wound site 18.

It will be appreciated that many modifications, improvements andequivalents may be made within the claimed scope of the invention.

1. An aspiration system for removing liquids other than urine, which liquids are discharged by the human body, the aspiration system comprising: a. a body interface device having a liquid collection region for collecting said liquid other than urine discharged by the human body; and b. a liquid sensor disposed or disposable adjacent to the liquid collection region, for detecting the presence of discharged liquid in the liquid collection region.
 2. The aspiration system according to claim 1, wherein the liquid sensor is configured to detect liquid without contact with the liquid.
 3. The aspiration system according to claim 1, wherein the liquid sensor generates an electronic signal indicative of sensed liquid.
 4. The aspiration system according to claim 1, wherein the body interface device is a disposable device.
 5. The aspiration system according to claim 1, wherein the liquid sensor is separate or separable from the body interface device.
 6. The aspiration system according to claim 1, wherein the liquid sensor is permanently attached to the body interface device.
 7. The aspiration system according to claim 5, wherein the liquid sensor is configured to be used a plurality of times with different body interface devices.
 8. The aspiration system according to claim 5, further comprising an attachment part for detachably attaching the liquid sensor to the body interface device.
 9. The aspiration system according to claim 1, further comprising a garment wearable over the body interface device, the garment being configured to hold the liquid sensor captive in an operative sensing position adjacent to the body interface device.
 10. The aspiration system according to claim 1, wherein the body interface device comprises a wound dressing for a wound site.
 11. The aspiration system according to claim 1, wherein the liquid sensor is selected from: a capacitance sensor; an ultrasonic sensor; a piezo-electric sensor; an electro-optic sensor; and a temperature sensor.
 12. The aspiration system according to claim 1, wherein the body interface device comprises a pocket or recess for receiving the liquid sensor adjacent to the liquid collection region.
 13. The aspiration system according to claim 11, wherein the liquid sensor is a capacitance sensor, and wherein the body interface device comprises a wall or wall portion made of material through which the capacitance sensor can project an electric field.
 14. The aspiration system according to claim 11, wherein the liquid sensor is an ultrasonic sensor, and wherein the body interface device comprises a wall or wall portion made of material through which an ultrasonic wave can be passed.
 15. The aspiration system according to claim 11, wherein the liquid sensor is an electro-optic sensor, and wherein the body interface device comprises a wall or wall portion made of material through which optical radiation can be passed.
 16. The aspiration system according to claim 1, further comprising a skin adhesive for releasably attaching the body interface device to the body.
 17. The aspiration system according to claim 1, further comprising a liquid handling material within the liquid collection region, the liquid handling material comprising at least one selected from: a non-gelling liquid absorbing material; and a gelling liquid absorbing material.
 18. The aspiration system according to claim 17 comprising a first region of gelling liquid handling material facing an opening of the body interface device, and a second region of non-gelling liquid handling material disposed on the opposite side.
 19. An aspiration system for removing liquid other than urine, which liquid is discharged by the human body, the system comprising: a liquid sensor configured to detect said liquid other than urine discharged from the body in the proximity of the sensor without contact with the liquid, the sensor generating an electrical output indicative of detected liquid, and the sensor being selected from: a capacitance sensor; an ultrasonic sensor; a piezo-electric sensor; an optical sensor.
 20. The aspiration system according to claim 19, further comprising a body interface device having a liquid collection region for receiving the liquid other than urine, and wherein the liquid sensor is disposed outside the liquid collection region and configured to detect urine within the liquid collection region.
 21. The aspiration system according to claim 20 wherein the body interface device comprises a wound dressing, and the liquid other than urine is wound exudate.
 22. The aspiration system according to claim 21, further comprising an aspiration unit responsive to the output from the liquid sensor, and configured to generate suction to aspirate liquid from the body interface device when liquid is detected by the liquid sensor.
 23. A wound dressing comprising a liquid sensor is configured to detect liquid discharged from the body in the proximity of the sensor without contact with the liquid, the sensor being selected from: a capacitance sensor; an ultrasonic sensor; a piezo-electric sensor; and an optical sensor.
 24. The wound dressing of claim 23, wherein the liquid sensor is disposed adjacent to but outside a liquid collection region of the wound dressing for collecting exudate discharged from a wound, and is configured to detect the presence of exudate in the liquid collection region.
 25. A method of preparing an aspiration system for removing liquid other than urine, which liquid is discharged by the human body, the method comprising: a. providing a body interface device having a liquid collection region for receiving said liquid other than urine discharged by the human body; b. providing a liquid sensor for detecting the presence of discharged liquid in the liquid collection region; c. providing an aspiration unit couplable to the body interface device and to the liquid sensor, the aspiration unit being operable to generate suction to aspirate liquid from the body interface device in response to the liquid sensor.
 26. The method of claim 25, wherein the liquid sensor is separate or separable from the body interface device.
 27. The method of claim 25, wherein the liquid sensor is permanently attached to the body interface device.
 28. The method of claim 25, wherein the liquid sensor is a non-contact sensor for detecting the liquid without contact with the liquid.
 29. The method of any of claims 25, wherein the body interface device is a wound dressing, and the liquid other than urine is wound exudate.
 30. The method of any of claims 25, wherein the liquid sensor is selected from: a capacitance sensor; an ultrasonic sensor; a piezo-electric sensor; an electro-optic sensor; and a temperature sensor. 